The GOP field to challenge Shaheen is sparse, but there's no shortage of ambitious local Republicans considering the race. Republicans frequently cite the following as possible candidates: former Sen. John E. Sununu, his brother, New Hampshire Executive Councilor Chris Sununu, and former Reps. Frank Guinta and Jeb Bradley.

On Thursday evening, Brown refused to rule out challenging Shaheen, telling reporters, "I don't think I'm done with politics" after he delivered a speech to a dinner commemorating Martin Luther King Jr.

Local GOP reaction to a potential Brown bid is mixed. One top New Hampshire GOP operative privately cautioned Brown would have a primary if he runs.

"I know he's a former senator, but he is still more to the left than a lot of Republicans are," said the operative, requesting anonymity to speak candidly. "There is a possibility that someone who is more of a traditional conservative could run. He's going to have to deal with that carpetbagger (charge)."

And it's unclear if any of the aforementioned potential candidates would forgo their own bid if Brown runs in New Hampshire. Bradley did not rule out a run in an interview with CQ Roll Call, citing a focus on his current duties as state senate majority leader.

"We’ll see about the future when that takes care of itself," Bradley said. "I like Scott ... He's a senator from Massachusetts. We wish him well, and we'll see what happens."

Meanwhile, New Hampshire GOP Chairwoman Jennifer Horn wrote a fundraising email Friday afternoon to committee supporters railing against Shaheen's economic policies. Horn did not mention Brown, or his speech last night.

To be sure, some Granite State Republicans praised Brown and his campaign activities in New Hampshire, specifically in support of Republican Sen. Kelly Ayotte in 2010.

“I would say that Scott Brown has more connections to New Hampshire than Hillary Clinton had to New York when she first ran for Senate," New Hampshire Republican Jim Merrill said.

Democratic National Chairwoman Debbie Wasserman Schultz will speak to state Democrats in Manchester, N.H. this weekend. Wasserman Schultz, a Florida Democrat, will likely mention Brown's interest in the race in her remarks, according to a DNC source, in a jocular reference to his famous pickup truck crossing state lines.

Brown's comments were particularly surprising given he has shown little interest publicly in running for office again in the Bay State since he lost his re-election last November.

Earlier this year, Brown declined to run in the special election to replace former Sen. John Kerry, D-Mass., who is now secretary of state. In the last two months, Brown has signed on as a contributor to FOX News and joined a Boston law firm.

Brown anchored "The O'Reilly Factor" earlier this week. Should he get serious about running, he will likely have to consider his commitment to that network. Fox News suspended the contracts of Newt Gingrich and former Sen. Rick Santorum in 2011 when each had "demonstrated that they are seriously running for president," per the Los Angeles Times.

Update 4:14 p.m.

New Hampshire GOP Chairwoman Jennifer Horn had this to say about a Brown bid in an email response to to Roll Call:

"NH Republicans are accustomed to competitive primaries and I am sure that if Scott Brown decides to come to NH the voters will listen to what he has to say and give him an honest chance," Horn said.